IS-IS
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Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this by determining the best route for data through a packet switching network.
The IS-IS protocol is defined in ISO/IEC 10589:2002
In 2005, IS-IS was called "the de facto standard for large service provider network backbones."[4]
Description
IS-IS is an interior gateway protocol, designed for use within an administrative domain or network. This is in contrast to exterior gateway protocols, primarily Border Gateway Protocol (BGP), which is used for routing between autonomous systems (RFC 1930).
IS-IS is a link-state routing protocol, operating by reliably flooding link state information throughout a network of routers. Each IS-IS router independently builds a database of the network's topology, aggregating the flooded network information. Like the OSPF protocol, IS-IS uses Dijkstra's algorithm for computing the best path through the network. Packets (datagrams) are then forwarded, based on the computed ideal path, through the network to the destination.
History
The IS-IS protocol was developed by a team of people working at
IS-IS was developed at roughly the same time that the Internet Engineering Task Force
Packet types
IS-IS adjacency can be either broadcast or point-to-point.
- Hello Packet
- The IS-IS hello packets needs to be exchanged periodically between 2 routers to establish adjacency. Based on the negotiation, one of them will be selected as DIS (Designated IS). This hello packet will be sent separately for Level-1 or Level-2.
- LSP
- This contains the actual route information. This LSP can contain many type–length–values (TLVs).
- CSNP
- This packet will be sent only by the DIS. By default for every 10 seconds, CSNP packet will be transmitted by DIS. This will contain the list of LSP IDs along with sequence number and checksum.
- PSNP
- If the router which receives CSNP packet finds some discrepancy in its own database, it will send an PSNP request asking the DIS to send specific LSP back to it.
Other uses
IS-IS is also used as the control plane for
Related protocols
References
- ^ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 10 March 2023.
- ^ "ISO/IEC 10589:2002 – Information technology – Telecommunications and information exchange between systems – Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)". ISO website. International Organization for Standardization (ISO). November 2002. Retrieved May 24, 2017.
- ^ "Free-of-charge PDF copy of ISO/IEC 10589:2002". ISO website. International Organization for Standardization. Retrieved May 24, 2017.
- ISBN 1-85233-822-9.
- doi:10.17487/RFC6329.
External links
- IS-IS standard (ISO/IEC 10589:2002, Second Edition) – free-of-charge PDF version
- RFC 1195 – Use of OSI IS-IS for Routing in TCP/IP and Dual Environments
- OSPF and IS-IS: A Comparative Anatomy by Dave Katz, Juniper
- Collection of RFCs pertaining to IS-IS Archived 2013-06-02 at the Wayback Machine
- IS-IS and OSPF difference discussion (Vishwas Manral, Manav Bhatia and Yasuhiro Ohara)
- Google Quagga IS-IS implementation
- Sample isisd.conf file: used with Quagga